X-ray Binaries in Nearby Galaxies
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X-ray Binaries in Nearby Galaxies
Vicky Kalogera Northwestern University
• Super Star Clusters
• Starburst galaxies
• Ultra-Luminous X-Ray Sources
• Elliptical galaxies
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Chandra observations of XRBs - some of the puzzles -
How does XRB formation and evolution depend on star-formation history and metallicity ?
Do Super Star Clusters form High-Mass XRBs ?
What determines the shape of X-Ray Luminosity Functions (XLF) ? Is it due to a blend of different XRB populations ?
What is the nature of Ultra-Luminous X-ray Sources (ULX) ?
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Super-Star Clusters (SSCs)
• Compact, young analog to globular clusters• Found frequently in starburst environments
• Masses range from ~104 to ~106 M
•Ages range from a few to tens of Myr
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Kaaret et al. 2004
• Lx ≥ (0.5-3)x1036 erg/s
Distribution of X-Ray point sources
< 1 XRB per cluster!
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Kaaret et al. 2004
• Lx ≥ 5x1035 erg/s
Distribution of X-Ray point sources
• XRBs closely associated with star clusters• Median distance ~30-100 pc
< 1 XRB per cluster!M82N5253
N1569
50%
Is this all due to Is this all due to Supernova Kicks ?Supernova Kicks ?
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Theoretical XRB Distributions
• cluster mass: ~5x104 Mo
• LX > 5x1035 erg/s• average of 1,000 cluster simulations
• Significant age dependence
• < 1 XRB per cluster
Models: Population Syntheses of XRBs and Kinematic Orbit Evolution in Cluster Potential
Sepinsky et al. 2005, ApJL
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Conclusions
XRB models without cluster dynamics appear in agreement with observations
Mean XRB number per SSC < 1 and spatial distribution: M < 105 Mo and 10-50Myr or more massive and ~50Myr
• Results do not appear sensitive to binary evolution assumptions, but extended parameter study is needed.• Explore role of dynamics for more massive and older clusters
Supernova kicks: eject XRBs @ D > 10pc especially for M < 105 Mo
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NGC 1569NGC 1569(post-)starburst galaxy at 2.2Mpcwith well-constrained SF history: > ~100Myr-long episode, probably ended 5-10Myr ago, Z ~ 0.25 Zo
> older population with
continuous SF for ~ 1.5Gyr, Z ~ 0.004 or 0.0004, but weaker in SFR than
recent episode by factors of >10
Vallenari & Bomans 1996;Greggio et al. 1998;Aloisi et al. 2001; Martin et al. 2002
courtesySchirmer, HST
courtesyMartin, CXC,NOAO
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Belczynski, VKet al. 2004, ApJL
NGC 1569 XLF modeling
Hybrid of 2 populations:
underlying old starburst young
Old: 1.5 GyrYoung: 110 MyrSFR Y/O: 20
Old: 1.5 GyrYoung: 70 MyrSFR Y/O: 20
Old: 1.3 GyrYoung: 70 MyrSFR Y/O: 40
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Conclusions on Starbursts
Current understanding of XRB formation and evolution produces XLF properties consistent with observations Model XLFs can be used to constrain star-formation properties, e.g., age and metallicity
Shape of model XLFs appear robust against variations of most binary evolution parameters
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Ultra-Luminous X-ray Sources
First discovered with Einstein X-ray telescope
Extragalactic sources with LX ≥ 1039 erg/s
Later observations determined many are off-nuclear & not associated with supernovae
What is the origin of these sources?
Intermediate-Mass Black Holes? (50 - 1000Mo)
Strongly Anisotropic XRB emission ?
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IMBH Binaries ?
Cluster core simulations with binary evolution and multi-body dynamical interactions
Do IMBH acquire mass-transfering binary companions in cluster cores ?
Blecha, Ivanova, VK et al. 2005
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IMBH Companions
Mass Mass distributiondistribution
Orbital separation Orbital separation distributiondistribution
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Conclusions on IMBH Binaries
• Optimal IMBH mass range: 100-200 Mo
• MT is relatively rare; highest incidence at 100Mo
about 3-5% of cluster lifetime with MT IMBH binary
• MS mass-transferring companions are more common & spend more time in MT
BUT ARE THEY ULXs?Blecha, Ivanova, VK et al. 2005
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Brightest XRBs in Elliptical Galaxies
Upper-end XLF slope (LX: from ~0.5 - 2 1039 erg/s) :
footprint of accreting BH mass spectrummodified by probability of XRB detection due to
transient mode of accretion
Ivanova & VK 2005, ApJ
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What to Expect in the Future ?
For example:
* Long-term time monitoring will become possible; identification of X-ray transients and clues to ULX nature
* Bigger source samples will allow probing the rarebrightest sources and questions of BH formation
* Systematic modeling of galaxy samples will reveal sensitivity to SFR and Z …